Devices, such as printers, which connect to a computer are well known. A computer has many different known ways (or interfaces) for the device to connect to it. Two such interfaces are the Universal Serial Bus (USB) interface and the Ethernet interface. The USB interface provides a way for the device to directly connect to one computer. The Ethernet interface is a network interface which provides a way for the device to connect to any computer on the network. Known devices, such as some printers, include those having both USB and Ethernet interfaces. The USB and Ethernet interfaces operate at different speeds and require different clock speeds. The USB interface requires a 48 megahertz (MHz) clock to operate. The Ethernet interface physical layer (PHY) that controls the signaling rate on the network requires a 25 MHz clock frequency to operate.
One known method to provide the different clock frequencies to the USB and Ethernet interfaces of the same device is to provide two clock sources such as two resonators or crystals. In this method, a 48 (or 24 which is later doubled) MHz crystal or resonator is used to drive the USB interface, and a 25 MHz crystal or resonator is used to drive the logic of the PHY of the Ethernet interface. The USB interface logic is usually implemented in a digital application specific integrated circuit (ASIC). This method requires two relatively expensive crystals or resonators on the printed circuit board (PCB) of the device.
Another known method to provide the different clock frequencies to the USB and Ethernet interfaces of the same device is to use one clock source to drive two separate phase lock loop circuits in a digital ASIC. The first phase lock loop circuit is dedicated to the 48 MHz clock frequency for the USB interface, and the second phase lock loop circuit is dedicated to the 25 MHz clock frequency for the PHY of the Ethernet interface. Because a phase lock loop circuit is an analog structure, it takes up a significant portion of the digital ASIC die size requiring a larger die size which increases costs.
What is needed is an improved method for providing different clock frequencies for different interfaces of a device.